Milling & Machining Fixtures: Everything You Need to Know

Milling and machining fixtures play an essential role in the world of manufacturing.

Helping to improve machining processes by making them more efficient, safe and accurate, the advantages of work holding fixtures are vital in modern manufacturing.

In an industry defined by efficiency and quality, milling and machine fixtures are fundamental in production processes. Despite suffering setbacks from the pandemic, the manufacturing industry in the United States has a predicted growth rate of 9.8% throughout 2021 and a market size of $6 trillion.

To learn more about the fundamentals, advantages and types of milling and machining fixtures, our article will explain it all.

What is a Milling Fixture?

Milling is a machining operation where cutters rotate to remove material in the direction of the angle from the workpiece.

Essential to milling machines are jigs and fixtures. 

Milling fixtures, or fixtures, are strong and rigid work-holding devices firmly clamped to the table of a milling machine. The purpose of fixtures is to secure workpieces in the correct position as the table moves past cutters.

While often used synonymously with fixtures, jigs are work holding devices that hold, support and locate a workpiece while guiding the cutting tool. Jigs are typically lighter in construction and don’t require gauge blocks like fixtures sometimes do.

One alternative to single-purpose fixtures used in mass production is modular fixtures.

A modular fixture is constructed from a kit of interchangeable components, allowing multi-purpose milling and better cost-saving opportunities. When modular fixtures aren’t in use as a workholding solution, they can be easily dismantled for storage.

Components of Workholding Fixtures

While jigs and fixture plates are standard to most CNC mill workholding devices, fixtures are more frequently used with milling operations because they’re more accurate. From there, the structure of a workholding fixture dictates its function. Now regardless of the task at hand, there are four main components of a CNC fixture.

These components are as follows:

Fixture Body

Fixture bodies are used to secure fixtures to a worktable.

In CNC workholding fixtures, there are four main types of fixture bodies, including:

• Angle Plates – Two perpendicular plates that are sometimes customizable
• Tombstones – Large, vertically-oriented rectangular fixtures with two sides that can position multiple workpieces perpendicular to a worktable
• Baseplates – Mountable worktable fixtures commonly used in milling and drilling
• Faceplates – Where components are secured to a faceplate then mounted onto a spindle (mostly used in lathe processes)

Locators

Locators are used for establishing and maintaining the position of a workpiece in a fixture or jig.

There are four main types of locators in milling, these include:

• Fixed Locators – Locators fixed into a fixture
• Integral Locators – Heavy-duty locators built into the fixture
• Assembled Locators – May be attached and removed from the fixture
• Adjustable Locators – Permits movement through threads or springs that are adjustable to a workpiece’s size

Supports

Supports vary in shape and size and are available as fixed, adjustable, assembled and integral.

As their name suggests, supports aid the workpiece during the machining process by helping to prevent deformation. Depending on the geometry of the workpiece, supports are commonly located beneath the workpiece and are where the cutting tool will make contact.

Additionally, it’s not uncommon to find multiple supports with a single CNC work holding fixture.

Clamps

Clamps are used for strengthening or holding things together and are hydraulic or pneumatic.

For machining processes that require larger workpieces, hydraulic clamps are frequently used as they consume less space than pneumatic clamps.

On the other hand, machining operations that use smaller workpieces tend to leverage pneumatic clamps as they:

• Are portable and economic to use
• Provide uniform pressure on the part
• Can be quickly activated and deactivated thereby saving changeover time

Unlike hydraulic clamps that compress a liquid for generating grip force, pneumatic clamps compress a gas (usually air) to attain gripping power. Additional types of clamps commonly used in milling include toggle, angle and vice jaw clamps.

How Machining Fixtures Work

The core purpose of a machining fixture is determined by the fixture design.

In CNC machine milling, there are many fixtures applicable to making certain fixtures better than others for specific machining processes. That’s why depending on the type of milling required, injection molding or 3D printing are sometimes used over custom CNC.

Factors that influence these decisions include:

• Lead costs
• Materials
• Volume
• Speed

So, how do fixtures work?

The body, locator, supports and clamps of a milling fixture work as one to position, secure and guide a workpiece through the machining process while withstanding the large cutting force.

Benefits of Jigs and Fixtures

Jigs and fixtures play a crucial role in mass production from helping manufacturers produce more economically with less waste to helping organizations attain new levels of efficiency with fewer errors.

Additional benefits machining jigs and fixtures offer are:

• Cost Reduction – Increase your production output through more effective processes
• Productivity – Eliminate the need for individual marketing, positioning and checking while increasing the speed, feed and depth of a cut due to high clamping rigidity
• Interchangeability – Facilitate large quantities of articles with precision and uniform quality
• Skill Reduction – Unskilled and semi-skilled machine operators are capable of operating jigs and fixtures allowing savings in labor costs
• Increased Production Capacity – Simplify the assembly process, reduce non-productive hours and automate a machine tool to a certain extent
• Improved Quality Control – Inspection and quality control expenses are less significant while improved safety standards decrease incident frequency

Manufacture Work Holding Fixtures with Precision

Manufacturers rely on machining fixtures to mitigate errors, streamline efficiency and reduce labor costs. Without milling fixtures and jigs, mass production would not be what it is today.

As with all production machining, quality and depth of service are foundational to improving your manufacturing processes.

For comprehensive full-service production machining with inclusive supply chain management, Moseys is your one-stop-shop for assembly-ready machined parts.

As a third-generation family business, we believe in the value of providing impeccable service and top-notch quality. With 99.1% of orders delivered on time or ahead of schedule, our track record and over 46 years of business serve as a testament to our services.

To learn more, speak with one of our specialists today.